TECHNICAL FIELD

Described herein is an assembly to control or govern relative speed of movement between parts. More specifically, described herein is an assembly that uses eddy current formation to control or govern the relative speed of movement between two parts.

BACKGROUND ART

Eddy current formation may be used in a variety of ways to adjust the speed of rotation of a member. Various apparatus exist, for example in abseiling, to control the descent of a climber or for example, in personal protective equipment scenarios to prevent an injury causing fall. Other applications that use eddy current generation are in controlling payout of line in trains, cable cars, zip line devices and roller coasters.

One art device is published as US2012/0055740. This device utilises a rotor assembly. The rotors themselves may be conductive or magnetic or may have conductive or magnetic members attached thereto. When a rotational force is applied, the rotors move outwards from a central axis via centrifugal force and into a magnetic (or conductive) field. As the rotors move through the field, eddy currents are generated, the strength of which is proportional to the speed of rotation. As the speed of rotation reduces, the rotors are drawn back towards the axis of rotation via springs. This device is widely used however requires a number of moving parts. Another disadvantage is that, when the rotors move outwards and the field is generated, the magnetic field is not continuous around the circumference of the spin axis hence does not provide a continuous eddy current generation path.

As may be appreciated, reducing the number of parts in mechanical assemblies may be an advantage so as to reduce assembly cost. In addition, moving parts in mechanical assemblies generally require more maintenance and hence cost more. Minimising the number of moving parts may be advantageous. Maximising eddy current force generation may also be an advantage or at least it may be useful to provide the public with a choice.

Further aspects and advantages of the assembly and methods of use thereof will become apparent from the ensuing description that is given by way of example only.

SUMMARY

Described herein is an assembly and methods of use thereof for controlling or governing the relative speed of motion between the assembly parts via eddy current formation. The assembly and methods may also minimise the number of parts required and may minimise the number of moving parts thereby increasing the mechanical durability of the assembly compared to art designs that may have more moving parts and greater complexity.

In a first aspect, there is provided an assembly comprising:

a tube including a wall and void defined therein; and

a cylinder that fits into the tube void;

wherein, in use, the cylinder and tube have different relative speeds of rotation to each other and wherein the tube and cylinder or a part thereof interact to alter an eddy current induced braking force against different relative speed of motion with modulation of braking force arising due to a balance of the forces on the tube and cylinder.

In a second aspect there is provided an assembly substantially as described above wherein the axis and rotation of the tube and/or cylinder is linked to a shaft which may in turn be linked to a spool of line and wherein the speed control assembly regulates the speed of pay out of the line from the spool.

In a third aspect there is provided a method of braking the fall of an object by the step of linking the object or objects to a spool of line which in turn is linked to the assembly substantially as described above and allowing the object or objects to fall through gravity thereby creating a torque force on the shaft which in turn causes the speed control assembly to create a braking force on pay out of the line from the spool.

In a fourth aspect, there is provided a fall protection safety device including an assembly substantially as described above.

In a fifth aspect, there is provided an assembly substantially as described above wherein the assembly is incorporated into a zip line amusement ride to control the acceleration and deceleration of a suspended zip line passenger chair connected to a cable linked with the speed control system.

The inventor's have devised an apparatus where the various components interact to alter an eddy current induced braking force with modulation of braking force arising due to a balance of the forces on the tube and cylinder determining the extent of force applied.

Advantages of the above include the provision of an assembly and method with few moving parts that still provides an efficient use and transfer of eddy current forces to control or govern the relative speed of movement of parts in the assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the assembly and methods of use thereof will become apparent from the following description that is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of one embodiment of the assembly using a lead screw shaft with the parts in a non-braking alignment;

Figure 2 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of an alternative embodiment of the assembly using a driving ramp on the shaft with the parts in a partial braking alignment;

Figure 3 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of an alternative embodiment of the assembly using a bias mechanism;

Figure 4 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of an alternative embodiment of the assembly using an alternative bias mechanism;

Figure 5 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of an alternative embodiment of the assembly using a driving ramp on the shaft and bias mechanism with the parts in a partial braking alignment;

Figure 6 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of one embodiment of the assembly using a lead screw shaft and a weight with the parts in a partial braking alignment;

Figure 7 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of one embodiment of the assembly using a lead screw shaft, weight and bias mechanism with the parts in a partial braking alignment;

Figure 8 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of one embodiment of the assembly using a ramp and weight arrangement with the parts in a partial braking alignment;

Figure 9 illustrates a perspective view [A], a side view [B], a front view [C] and a side section view [D] along section line AA of one embodiment of the assembly using a ramp, weight arrangement and bias mechanism with the parts in a partial braking alignment;

Figure 10 illustrates alternative shapes of cylinder and tube that may be used;

Figure 11 illustrates a cross-section side view of a tube and cylinder design using multi-layer

concentric walls;

Figure 12 illustrates an alternative cross-section side view embodiment of a tube and cylinder design using multi-layer concentric walls with varying magnet positions to that shown in Figure 11; and,

Figure 13 illustrates a further cross-section side view multi-layered concentric wall embodiment. DETAILED DESCRIPTION

As noted above, described herein is an assembly and methods of use thereof for controlling or governing the relative speed of motion between the assembly parts via eddy current formation. The assembly and methods also may minimise the number of parts required and may minimise the number of moving parts thereby increasing the mechanical durability of the assembly compared to art designs that may have more moving parts and greater part complexity.

For the purposes of this specification, the term 'about' or 'approximately' and grammatical variations thereof mean a quantity, level, degree, value, number, frequency, percentage, dimension, size, amount, weight or length that varies by as much as 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% to a reference quantity, level, degree, value, number, frequency, percentage, dimension, size, amount, weight or length.

The term 'substantially' or grammatical variations thereof refers to at least about 50%, for example 75%, 85%, 95% or 98%.

The term 'comprise' and grammatical variations thereof shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements.

The term 'tube' and grammatical variations thereof may in one embodiment refer to a cylindrical element having a circular hole or void that a circular cylinder mates with but also could be a square exterior tube wall and circular void or a polygonal tube wall (interior and exterior) or a frusto-conical tube wall.

The term 'cylinder' and grammatical variations thereof may refer to various shapes, a key criteria being the ability of the cylinder to move axially and/or rotationally relative to the tube void space or vice versa i.e. the tube may also move axially and/or rotationally relative to the cylinder. Note that the cylinder need not be solid and may have a void space or spaces therein.

In a first aspect, there is provided an assembly comprising:

a tube including a wall and void defined therein; and

a cylinder that fits into the tube void;

wherein, in use, the cylinder and tube have different relative speeds of rotation to each other and wherein the tube and cylinder or a part thereof interact to alter an eddy current induced braking force against different relative speed of motion with modulation of braking force arising due to a balance of the forces on the tube and cylinder.

The inventor's have devised an apparatus where the various components interact to alter an eddy current induced braking force with modulation of braking force arising due to a balance of the forces on the tube and cylinder determining the extent of force applied.

The cylinder may move relative to the tube via two separate degrees of movement being: (a) axial translation of the cylinder relative to the tube so that the cylinder can pass at least partially into or out of the tube void; and

(b) rotation of the cylinder relative to the tube about a longitudinal axis, the axis passing through the tube void.

Alternatively, the tube may move relative to the cylinder via two separate degrees of movement being:

(a) axial translation of the tube relative to the cylinder so that the cylinder can pass at least partially into or out of the tube void; and

(b) rotation of the tube relative to the cylinder about a longitudinal axis, the axis passing through the tube void.

Coupled to the tube and cylinder may be one or more conductive members and one or more magnetic members, the tube and cylinder each having either magnetic member(s) or conductive member(s) and the conductive members and magnetic members orientated to interact with each other.

The tube and cylinder may have a common axis of rotation. As noted above, the tube and cylinder may have varying cross sectional shapes and do not need to be circular. It is however anticipated that a circular void in the tube and similar mating circular cylinder cross-section would provide the greatest degree of efficiency hence this may be advantageous for most applications. With two nesting circular cross-sections, a common axis of rotation may be a useful feature.

The cylinder may rotate about a rotating member passing through the axis of rotation of the cylinder and tube. A rotating member may be a shaft, although other configurations may be possible. Other features may be included between the shaft and cylinder such as bearings. In an alternative embodiment, the tube may rotate about a rotating member such as a shaft.

The rotating member may include a helical groove in order to translate rotational movement of the member into linear movement of the cylinder. The helical groove pitch and/or lead may be varied in order to vary the brake response. The rotating member may be a lead screw. A helical groove may be used to control and/or drive axial movement of the cylinder. This is not essential as other methods may be used to control and drive axial movement such as different bias arrangements or different bearing face arrangements and a helical groove should not be seen as limiting.

The conductive member or members may be wider than the magnetic member or members. Whilst not essential, the greatest eddy current generation may occur when the conductive members are wider than the magnetic members so that a full-induced magnetic field is generated. Smaller conductive member regions may still be used but a smaller magnetic field may be generated in these circumstances leading to a reduced eddy current drag formation.

The gap between the magnetic and conductive members may be minimised in order to maximise the eddy current brake force. As may be appreciated, a large gap leads to a smaller magnetic field and less eddy current drag force generation. This may be advantageous in some circumstances however, to generate the greatest force for the least effort, a substantially small gap (less than approximately 5mm, or 4mm or 3mm, or 2mm, or less than 1mm) may be useful.

The tube may be fixed in place and the cylinder may move axially and rotationally relative to the tube. Opposite movement may be useful for example having the tube move via a motor towards or away from the cylinder but an aim of the assembly described herein is to minimise the overall number of parts required and also to minimise the number of moving parts.

The cylinder may rotate at a different relative speed to the tube in a co-current or counter-current direction. As may be appreciated, of key importance to generating eddy currents is a different relative rotational speed between the conductive member and magnetic member. One means of achieving this is to have the conductive member being the tube and the magnetic member being the cylinder and having each member rotate at a different relative speed. As noted above, the tube may be fixed in place and not rotate at all. The tube may also rotate in either the same direction (but at a different speed to the cylinder) or may rotate in the opposite direction to the cylinder (in which case a stronger eddy current force might result due to a greater relative speed difference).

The cylinder may be at least partially outside of the tube when the cylinder and/or tube are not rotating. The cylinder may be at least partially inside the tube when the cylinder and/or tube are not rotating. Varying the position of the cylinder axially when the assembly is at rest may alter the characteristics at start up of rotation. For example, if the cylinder is already in the tube, immediate eddy current drag force generation will occur when the cylinder (or tube) rotates. If the cylinder is outside the tube when rotation commences, minimal immediate eddy current force will occur - this delayed effect might be useful where a small amount of rotation is desired such as when a slow payout of line is needed in a climbing application. When a fall occurs, the pay out of line becomes much faster and that faster rate of rotation may then cause engagement of the cylinder and tube via axial translation to generate a drag force and brake effect.

Varying the at least one magnet member strength and/or position on the cylinder or tube may vary the brake response. Varying the at least one conductive member chemical composition and/or position on the cylinder or tube may vary the brake response. To further illustrate this feature, some art eddy current devices use spaced apart conductive or magnetic members. The result of this may be a lower level of eddy current generation than a continuous field. For example, the conductive member(s) may be moving rotationally in and out of a magnetic field hence they may only be creating a smaller or less efficient eddy current drag force than if the field were continuous. In contrast the described arrangement of a tube and cylinder means it may be possible to generate a continuous field between the conductive and magnetic members due to the continuous nature of the tube void surface and cylinder surface. One example of a completely continuous eddy current generating relationship may be to have the cylinder made entirely from a conductive member or at least the outer surface of the cylinder being made from or containing an electrically conductive member and the tube itself or outer surface of the tube void being made from or containing a magnetic member. A continuous interface is then created between the two parts for eddy current generation. Variations on this may also be undertaken where a less than continuous interface is desired however, the ability to create a continuous surface may be unique and an advantage of this particular design.

Varying the relative speed of rotation of the tube and cylinder may vary the brake response. As noted above, relative speed is key in generating eddy currents. Assuming the axial position of the cylinder and tube does not change and the conductive and magnetic members positioning does not change, a next way of altering the eddy current characteristics may be to change the relative rotation speed.

At least part of the cylinder may contain or may be formed from electrically conductive material and may thereby form a conductive member. At least part of the tube may contain or may be formed from electrically conductive material and may thereby form a conductive member. Conductive members may be placed onto the surface of the cylinder or tube and similarly, magnetic members may be placed on the surface of the cylinder or tube. The tube or tube void wall may itself be a conductor or magnetic material as can the cylinder itself or cylinder exterior.

Axial movement of the tube and/or cylinder may be actuated via at least one motor. A motor may be avoided to minimise parts and minimise moving parts in the overall assembly although could be incorporated if desired.

The assembly may include a bias member that creates a direct or indirect axial force on the tube and/or cylinder, biasing the tube and/or cylinder together or apart on rotation of the tube and/or cylinder. The bias member may be a spring or springs.

Axial movement of the tube and/or cylinder may be generated when the tube and/or cylinder rotates, the axial movement caused by a translation of centrifugal energy into axial translation. The tube and/or cylinder may include at least one weight off-set from the axis of rotation, that, on rotation of the tube and/or cylinder, may be subject a centrifugal force and, via a kinematic relationship, translates the centrifugal force into an axial force on the tube and/or cylinder thereby causing relative axial movement of the tube and/or cylinder. A lever converting rotational movement of the weight to axial movement of the cylinder or tube may act to form the kinematic relationship. The weight or weights may move at least partially radially on application of a centrifugal force. In an alternative embodiment, centrifugal outward movement of the weight or weights may cause an axial movement of the cylinder by acting on a ramp arrangement.

The tube and/or cylinder may also be formed as multiple layers, the cylinder for example having a hollow interior and mating with a tube that has outer walls at least partly extending over the outside of the cylinder and internal walls extending into the cylinder hollow interior either before, during or after relative movement of the tube and cylinder. The tube and cylinder may have multiple nesting concentric walls. Magnets and/or conductive members may be located on the cylinder walls and/or one or more of the tube walls (outer and/or inner). In a further embodiment, the cylinder may have multiple concentric wall layers mating with multiple concentric wall layers on the tube and magnets and/or conductive members placed on some or all of the wall layers.

In a second aspect there is provided an assembly substantially as described above wherein the axis and rotation of the tube and/or cylinder is linked to a shaft which may in turn be linked to a spool of line and wherein the speed control assembly regulates the speed of pay out of the line from the spool.

The above assembly may include a retraction mechanism that retracts paid out line back onto the spool when a pay out force is removed.

The braking force applied to pay out of the spool of line may be at a substantially constant speed for extension over a range of applied torque.

The assembly as described above may include a housing, the housing enclosing at least a portion of the assembly. A housing may be useful to weather proof the assembly and also to i mprove the aesthetics of the assembly. A housing may also be important for safety to avoid accidental injury.

In a third aspect there is provided a method of braking the fall of an object by the step of linking the object or objects to a spool of line substantially as described above and allowing the object or objects to fall through gravity thereby creating a torque force on the shaft which in turn causes the speed control assembly to create a braking force on pay out of the line from the spool.

The braking force may also reduce retraction speed of the line enough to allow a fully extended line with nothing attached to the line to cleanly retract.

The range of applied torque may cover objects attached to the line weighing about 9, or 10, or 11, or 12, or 13, or 14, or 15, or 20, or 25, or 30, or 35, or 40, or 45, or 50, or 55, or 60, or 65, or 70, or 75, or 80, or 85, or 90, or 95, or 100, or 105, or 110, or 115, or 120, or 125, or 130, or 135, or 140, or 145, or 150 kilograms. The range may be from about 9kg to about 150kg.

In a fourth aspect, there is provided a fall protection safety device including an assembly substantially as described above.

In a fifth aspect, there is provided an assembly substantially as described above wherein the assembly is incorporated into a zip line amusement ride to control the acceleration and deceleration of a suspended zip line passenger chair connected to a cable linked with the speed control system.

To summarise, control or governance of the relative speed of the members using the device described may occur as per the two examples A and B below:

[A] In the embodiment of a cylinder interacting with a shaft and tube where:

The two are connected in a manner wherein a kinematic relationship exists where relative rotation of the two along their axis is linked to a corresponding relative translational motion; Application of a torque on the shaft causes rotation of the shaft and thereby rotation of the cylinder; Rotation of the cylinder results in formation of a eddy current drag torque on the cylinder; and/or

An inertial torque is generated by the cylinder due to an applied rotational acceleration of the shaft;

- The kinematic relationship provides a corresponding axial force on the cylinder;

A biasing device may be connected between the shaft and cylinder whereby the bias is in relationship with the relative rotation of the shaft and cylinder, and the relative rotation of the cylinder and shaft reaches an equilibrium where the eddy drag torque and the inertial torque are balanced by the reaction torque of the bias device; or

- A biasing device is connected between the cylinder and a 'ground' body (possibly the tube or support structure), whereby the bias is in relationship with the relative translation of the shaft and cylinder, and the relative translation of the cylinder and shaft reaches an equilibrium where the induced axial force induced by the kinematic connection of the eddy drag torque and the inertial torque are balanced by the axial reaction force of the bias device; and

- The resulting equilibrium position of the shaft, cylinder, and tube provide a controlled eddy current induced braking torque based on the rotational speed and acceleration of the shaft; and The induced torque balances an applied torque.

[B] A cylinder interacting with a shaft wherein

- The two are connected in a manner wherein a kinematic relationship exists where relative translational motion is allowed and a centrifugal system is arranged to apply axial force on the cylinder upon rotation of the shaft; and

A biasing device is connected between the cylinder and a 'ground' body (possibly the tube or support structure), whereby the bias is in relationship with the relative translation of the shaft and cylinder, and the relative translation of the cylinder and shaft reaches an equilibrium where the centrifugally induced axial force is balanced by the axial reaction force of the bias device; and

The resulting equilibrium position of the shaft, cylinder, and tube provide a controlled eddy current induced braking torque based on the rotational speed and acceleration of the shaft; and - The induced torque balances an applied torque.

Advantages of the above assembly include the ability to control or govern relative speed of motion between the parts in an efficient manner that may also minimise the number of parts required and minimise the number of moving parts. Reducing the number of moving parts may increase the mechanical durability of the assembly since typically in mechanical devices, moving parts are where mechanical objects either fail or require maintenance (and hence cost more). The embodiments described above may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which the embodiments relates, such known equivalents are deemed to be incorporated herein as of individually set forth,

Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

WORKING EXAMPLES

The above described assembly and methods of use are now described by reference to specific examples.

EXAMPLE 1

Referring to Figures 1A-1D, one embodiment of the assembly is shown. The assembly 1 as illustrated includes a tube 2 with an inner 3A and outer wall 3B and a void 4 therein. The assembly 1 also includes a cylinder 5. The cylinder 5 moves relative to the tube 2 via two degrees of movement being an axial translation along arrow A into and out of the tube 2 void 4 and a rotational movement B relative to tube 2. Axial movement A can be completely or partially into or out of the void 4. In the embodiment illustrated, the tube 2 and cylinder 5 share a common central axis of rotation. The cylinder 5 may rotate in direction B about a shaft 7. The shaft 7 may have a helical groove thereon which, when the shaft 7 rotates in direction B, drives axial movement A of the cylinder 5 relative to the tube 2. The tube 2 and cylinder 5 may include one or more conductive members and magnetic members (not shown). In one embodiment, the conductive member(s) may be on the tube 2 or the tube 2 it self may be a conductive member and the magnetic member(s) may be on the cylinder 5 or the cylinder 5 itself may be a magnetic member. The opposite scenario may also be the case with the conductive member(s) on the cylinder 5 or the cylinder 5 it self may be a conductive member and the magnetic member(s) may be on the tube 2 or the tube 2 it self may be a magnetic member. In use, when the tube 2 and cylinder 5 have different relative speeds of rotation, eddy current drag forces are produced between the members 2, 5 resisting rotation when placed in close proximity. In one embodiment, the tube 2 may be fixed in position and the cylinder 5 rotates. When the cylinder 5 enters the tube 2, eddy current forces (not shown) create a drag force on rotation B of the cylinder 5 and the speed of rotation B reduces. As may be appreciated, an eddy current force does not necessarily stop all rotation B but arrests speed of rotation to a level related to the relative magnetic field produced by movement of the cylinder 5 in the tube 2 void 4. Fast relative rotational movement B may result in a strong brake force for example. In other embodiments, the tube 2 may also rotate in the same direction as the cylinder 5 (but at a different relative speed) or in a counter rotational direction to the cylinder 5. A noted above, the shaft 7 may have a helical groove driving axial movement of the cylinder 5. The helical groove may be a thread or may be a lead screw. The helical groove pitch and/or lead may be varied in order to vary the brake response. By way of example, the pitch and/or lead may be such that a small rotation of the shaft 7 causes a large axial translation A of the cylinder 5 leading to a quick braking force being applied as the cylinder 5 moves quickly into the tube 2 and an eddy current force is generated. The opposite may also be the case where pitch/lead is varied to only allow a slow axial A progression, therefore resulting in a slow braking response.

Figures 2A to 2D illustrate an alternative embodiment where axial movement of the cylinder 5 may be driven by a ramped surface 16 about an interface 13 in the cylinder 5. As the cylinder rotates 5, the cylinder 5 is forced into the void 4 of the tube 2. In this example, no helical thread is required on the shaft 7 in order to drive movement.

Figures 3A to 3D illustrate an alternative embodiment where axial movement of the cylinder 5 may be influenced also by a bias mechanism such as a spring 8. The spring 8 may be used to change the characteristics of the braking action. For example, the spring 8 may be biased to draw the cylinder S out of the tube 2. When rotation of the cylinder 5 slows sufficiently, the spring 8 in this embodiment may act to draw the cylinder 5 from the tube 2 and thus release the braking force. In an alternative embodiment, the spring 8 may be used instead to force the cylinder 5 into the tube 2 to maintain a braking force for a longer period of time or to speed the pace within which a braking force may be applied.

Figures 4A to 4C illustrate a further alternative biasing arrangement. The cylinder 5 in the assembly 1 shown may be attached to a bar or fixed cylinder section 18 with each distil end of the section 18 connected to two sides of the cylinder 5 via two bias members 23, 24. The connection points of the spring members on the cylinder 5 are offset relative to the connection points on the bar 18. When the cylinder 5 rotates, the offset reduces or disappears entirely effectively lengthening the distance between the bar 18 and cylinder 5 and forcing the cylinder 5 into the void 4. When rotation B slows or stops, the bias members 23, 24 draw the cylinder 5 back towards the bar 18 and to the offset at rest position.

Figures 5A to 5D show how the embodiment shown in Figures 2A to 2D may be combined with a bias such as a spring 8 to combine the effects of both a ramped 13 axial A displacement and a bias 8 axial A displacement.

Figures 6A to 6D illustrate how a centrifugal force component may also be used to change the characteristics of the assembly 1. In the example shown, a weight 11 may be connected to the cylinder 5. When the cylinder 5 rotates, the weight 11 also rotates and a centrifugal force acts on the weight in direction F. Via a kinematic relationship, centrifugal force F on the weight 11 may be translated into an axial force A on the cylinder 5 to push (or pull) the cylinder 5 into or out of the tube 2. The kinematic relationship may be via a lever arrangement 12. This means of adjusting the characteristics may be useful in certain embodiments.

Also as shown in Figures 6A to 6D, the shaft 7 may be attached to a spool 9 of line to which an object (not shown) such as a person may be attached. As a force is applied on the line and spool 9 in direction X such as the object falling due to gravity, line is paid out from the spool 9 causing rotation of the spool 9 and shaft 7 in direction B leading to the cylinder 5 moving into or away from the tube 2 void 4. By way of example, a person may be the object which falls from a height. Through gravity the spool 9 rotates as line is paid out from the spool 9. Rotation of the spool 9 causes rotation of the shaft 7 that in turn causes the cylinder 5 to enter the tube 2 void 4 that may be fixed in position. The differing rotational speeds of the tube 2 and cylinder 5 cause an eddy current drag force (not shown) to occur which thereby slows the fall of the person on the line.

Figures 7A to 7D illustrates the same centrifugal arrangement as in Figures 6A to 6D however with the inclusion of a bias 8 to assist with drawing in or forcing out the cylinder 5 from the tube 2 void 4.

Figures 8A to 8D illustrate an alternative method of forcing axial translation A to the cylinder 5 using both centrifugal force and a ramp method. When the shaft 7 rotates, the weight(s) 15 are forced to move outward in direction F thereby acting on the ramp surface 16 of the cylinder 5 causing an axial translation A of the cylinder 5. As rotation speed B decreases, the centrifugal force F acting on the weights 15 decrease and the cylinder 5 returns to a non-retracted position.

Figures 9A to 9D illustrate the same embodiment as in Figures 8A to 8D where a bias spring 8 is also used to change the axial movement A characteristics of the cylinder 5 into or out of the tube 2 void 4.

Figure 10 illustrates some further alternative tube 2 and cylinder 5 arrangements. The embodiments described above utilise a circular tube 2 with a circular void but the tube 2 may have any polygonal exterior shape such as a square shape. The tube 2 internal void shape may be circular as shown in earlier Figures could also be elliptical, square, hexagonal and so on. Similarly, earlier Figures show a circular cross-section cylinder 5 but the cylinder 5 may take various shapes and may also be hollow.

EXAMPLE 2

A multilayer wall approach may also be used.

As shown in Figures 11 to 13, the cylinder 50 is hollow 51 and mates with a tube 60 that has a complimentary hollow 61. The overlapping walls 52, 62 of the cylinder and tube may contain magnets and/or conductive members that allow variation in eddy current tuning to occur. Figures 11 and 12 illustrate a multilayer tube 60 nesting with a hollowed cylinder 50 and two alternate magnet 63 configurations on the tube walls 62. Figure 13 illustrates a multiwall 52, 62 approach where both tube 60 and cylinder 50 have multiple concentric walls 52, 62 that mate together.

Aspects of the assembly and methods of use have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the claims herein.